Virtual impactor
AssigneeLovelace Medical Foundation
InventorsHsu-Chi Yeh, Bean T. Chen, Yung-Sung Cheng, George J. Newton
Life of this patent
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Abstract
A virtual impactor having improved efficiency and low wall losses in which a core of clean air is inserted into the aerosol flow while aerosol flow is maintained adjacent inner wall surfaces of the focusing portion of the impactor. The flow rate of the core and the length of the throat of the impactor's collection probe, as well as the dimensional relationships of other components of the impactor adjacent the separation region of the impactor, are selected to optimize separation efficiency.
Claims16
In a virtual impactor for separating solid or liquid particulate matter in an aerosol flow into a coarse particle flow and a fine particle flow, the virtual impactor having an acceleration nozzle and a collection probe, each aligned about a predetermined linear axis, and a flow separation region therebetween;
- said acceleration nozzle comprising an inlet, a substantially narrower outlet orifice, and a flow focusing portion therebetween formed with an inner wall surface for flow of said aerosol adjacent thereto and shaped for converging said aerosol flow from said inlet toward the linear axis whereby said converged aerosol flows through said outlet orifice through said flow separation region;
- said collection probe having an inlet impaction opening centered on said linear axis;
- the improvement comprising:
- means for flowing gas of near zero or zero aerosol content into the center of said aerosol flow as a core of gas that converges with said aerosol flow and flows therewith through the outlet orifice of said nozzle encased by said aerosol while maintaining aerosol flow adjacent the inner wall surface of said focusing portion.
In a virtual impactor for separating solid or liquid particulate matter in an aerosol flow into a coarse particle flow and a fine particle flow, the virtual impactor having an acceleration nozzle and an annular collection probe, each aligned about a linear axis, and a flow separation region therebetween;
- said acceleration nozzle comprising an inlet, laminating means disposed in said inlet for laminar flow therethrough of said aerosol, an outlet orifice that is substantially narrower than said inlet and formed with an annular inner wall surface, and a flow focusing portion therebetween formed with an inner wall surface, having an angle relative to said linear axis in the range of about 20 degrees to about 60 degrees for flow of said aerosol adjacent thereto and for converging said aerosol flow from said inlet toward said linear axis whereby said converged aerosol flows through said outlet orifice to said flow separation region;
- said collection probe having an inlet impaction opening defined by a rounded shoulder and formed with an annular inner wall surface centered on said linear axis;
- the improvement comprising:
- core flow means comprising a conduit for flowing gas that is substantially free of aerosol in the center of said aerosol flow downstream of said laminating means at a flow rate that is at least 1.2 times the rate of said coarse particle flow, said laminating means being centered on said gas conduit to converge said core gas with said aerosol flow to flow therewith through the outlet orifice of said nozzle as a core encased by said aerosol while maintaining aerosol flow adjacent the inner wall surface of said focusing portion, the ratio of the following dimensions to the inner diameter of the nozzle outlet orifice at said separation region being as follows:
- length of the annular inner wall surface of the collection probe=at least 0.3,
- outer diameter of the collection probe at said separation region=less than 5.
- radius of the rounded shoulder of the impaction opening of the collection probe=at least 0.1, and
- outer diameter of the nozzle outlet orifice at the separation region=less than 5.
Dependencies are inferred from the claim text.